If you're that fussed and you REALLY feel bad then go ahead and apologise. You seem like a pretty nice guy, just be friendly and say that you're sorry if you wierded her out a bit, then just say goodbye and walk away. Don't ask her out, don't give her your phone number, don't hit on her.. just apologise and say goodbye, and be as friendly as possible. That way hopefully she'll see that you really just feel bad, you took no for an answer butthat you just wanted to clear that up. You'll both leave happy. Personally I wouldn't go back to say sorry but that's just me, we're all different. Maybe i'm just not that nice! lol